Thermostatic devices such as the thermostatically controlled gas valves for water heaters and the like must be calibrated for the desired response to predetermined temperatures. Usually, the calibration is performed at the factory although it may also be done after installation of the thermostatic device.
The typical thermostatically controlled gas valve for water heaters employs a rod and tube thermostat which is immersed in the water within the water tank. The thermostat is supported from the gas valve assembly which receives the operating rod of the thermostat abutted against a lever that is mounted in the valve assembly to transmit movement from the thermostat rod to a snap-acting valve actuation mechanism. The fulcrum end of the lever within the valve structure is mounted on a temperature adjustment screw. This temperature adjustment screw has a control shaft projecting exteriorly of the gas valve and receives an indexed control knob that registers with a water temperature dial so that rotation of the control knob advances or retracts the adjustment screw and changes the position of the fulcrum for the operating lever.
After assembly of the water heater thermostat, it is necessary to calibrate the response of the device to the temperatures indicated by the index marker on the control knob. This calibration requirement has been the subject of a prior patent, U.S. Pat. No. 3,794,312, which discloses a sleeve clamp which is mounted over the control shaft and which resiliently grips the control shaft when the control knob is mounted on the shaft. While this structure is a considerable improvement over prior devices, it is desirable to provide a simpler assembly having reduced manufacturing costs and a longer service life.